Neonatal injury and trauma, such as occurs in the neonatal intensive care unit (NICU), induces life-long changes in cognitive, sensory and affective function. Although the mechanisms are as-of-yet unknown, we believe that developmental alteration of the Amygdalar CRF is likely to be a common contributing mechanism. Anatomically, CRF+ positive cells in the Central Nucleus of the Amygdala project to the ventrolateral Periaqueductal Grey and the Lateral Hypothalamus, regions involved in a variety of nocifensive behaviors. In addition, Amygdalar CRF has been shown to be critical for the acquisition or expression of both fear and pain, and the amygdala CRF system appears to be particularly sensitive to neonatal trauma. To investigate this, our lab has recently adapted a ?two-hit? paradigm to produce a trauma phenotype. First, modeled after practices in the NICU, neonatal rat pups are exposed to multiple paw punctures daily for the first week of life. Second, at one of four developmental stages (infancy, weaning, adolescence or adulthood) rats are exposed to a traumatic fear conditioning procedure. Our preliminary data show two sets of behavioral changes, which appear to differ in developmental timecourse. First, weanling rats exposed to both neonatal trauma and fear conditioning show a tactile hypersensitivity following fear conditioning, that cannot be explained solely by age, neonatal trauma or fear conditioning alone. Second, a sizeable subpopulation (~25-33%) of neonatal pain subjects show impaired freezing following fear conditioning later in life. This effect is present following weaning and strengthens as a function of age. The current proposal further examines these effects over 3 specific aims. In aim 1, we further examine the behavioral heterogeneity in response to neonatal pain by examining additional painful stimuli (inflammatory paw injections), additional activating stressors (restraint) and additional behavioral outcomes (non-conditioned anxiety tests; non-reflexive pain behaviors). In aim 2, we examine whether changes in amygdalar CRF can explain the observed behavioral changes. For example, CRF expression levels following both neonatal and activating stress will be observed using PCR and unbiased stereology. Newly created CRF-Cre rats crossed with a TD-tomato reporter line will be used to examine changes in circuit anatomy, with additional labeling of FOS used to examine changes in CRF+ cell activation. Tract tracing tools will be used to determine whether distinct projections of this system are differentially affected. In aim 3, we manipulate the Amygdalar CRF system in an attempt to reverse the neonatal trauma- induced phenotype. Systemic and local injections of CRF antagonists and agonists will be used during both the neonatal and activating stress in order to reverse the hypersensitive and affective phenotypes. In addition, chemogenetic approaches can be used with CRF-Cre rats to disrupt or enhance CRF projections to specific targets. Together, these experiments will definitely test the hypothesis that neonatal trauma affects subsequent behavior via alternations in CRF signaling in the Amygdala.